On what appears to be a routine recon mission, Daniel touches an artifact known as the Quantum Mirror and ends up in an alternate universe version where he never joined the Stargate Program, Sam is a civilian, Teal'c is still Apophis' First Prime since alternate!SG-1 never went to Chulak, Jack is a giant douchebag who obviously didn't undergo the character development he went through in Stargate, Abydos and eventually Chulak are destroyed, and the 'SGC' is the 'SGA'.
Alternate!SGA is promptly invaded and destroyed by the Goa'uld, the alternate versions of SG-1 all die, and due to their sacrifice Daniel makes it back to his reality with vital information: Apophis is planning an invasion of Earth.
"There But For The Grace Of God" provides examples of the following tropes:
- Alternate Universe: The episode to introduce the concept, which would be at revisited several points throughout the series' run.
- Bittersweet Ending: The alternate universe falls to the domination of the Goa'uld, but Daniel is able to escape with the information that could prevent his reality from suffering the same fate. Also the SGA self destruct has likely destroyed the landed mothership, putting a significant dent in the forces invading alternate Earth. Not that it’s likely to make much difference.
- Chekhov's Gun: The grenade from Daniel's pack, which alt!Carter uses to blow up herself and several Jaffa.
- Cliffhanger: It's revealed that Apophis is about to launch a full-scale attack against Earth.
- Dead Alternate Counterpart: Daniel (reasonably) assumes that his alternate counterpart must be dead, as his last known location was recently bombed by the Goa'uld. By the end of the episode, the alternate versions of all the other major characters have joined him.
- Disconnected by Death: The SGA are in contact with Air Force One until the plane is downed by a Goa'uld mothership.
- Expendable Alternate Universe: Daniel manages to convince the alternate universe characters to help him get home; they all end up dying as a result, and it's reasonable to assume that Earth is destroyed. Though to his credit, Daniel offered to return through the mirror with reinforcements from his own reality, and only suggests the more selfish alternative because the invasion has already reached a point where nothing this version of his friends can do would make much difference.
- Face Death with Dignity: Almost all of the alternate main characters do this. Particularly alternate Teal’c as he stands calmly in the Gateroom whilst the auto destruct counts down to zero.
- "Facing the Bullets" One-Liner:Alt!Carter: Oh yeah, I also wish to blow us all to hell.
- Fling a Light into the Future: Two of them.
- The unknown alien race that sent the 'beware the destroyer' message and provided the location for the invasion's staging point.
- Daniel manages to convince alternate O'Neill, Carter, and Langford that, while their universe's battle with the Goa'uld is lost, they can still help save his reality from suffering the same fate. The remaining SGA personnel sacrifice themselves to allow him to return to his reality with a warning about the coming invasion.
- Heroic Sacrifice: The alternate O'Neill, Carter, Hammond and Catherine Langford each get one in order to buy Daniel enough time to get back to his own reality.
- I Surrender, Suckers: Alt!Carter pulls this when she's cornered by the Jaffa, telling them she has valuable information she can share before pulling out a grenade and suicide-bombing them all.
- Last Stand: The defense of Cheyenne Mountain becomes this, as there is no hope of escape for those trapped inside. Only Daniel makes it out alive and even then he gets shot on the way out.
- Narrow Annihilation Escape: Daniel is able to dial and get back to the planet where he found the quantum mirror, just after he is shot [non-fatally] by Alt!Teal'c, as the base self-destruct is counting down the final 10 seconds.
- Nice Job Breaking It, Hero: Alt!O'Neill is unable to convince Teal'c to switch sides as he had previously sent a bomb to Chulak, killing Teal'c's wife Drey'auc and son Rya'c.
- Nuke 'em: The above-mentioned nuking of Chulak, ordered by alt!O'Neill in the hopes of making a dent in Apophis' forces, despite Daniel's protests that the Jaffa have been enslaved.
- Ominous Floating Spaceship: The mothership hovering over Cheyenne Mountain. Until it lands.
- Ominous Message from the Future: More like "ominous message from an alternate reality"; Daniel is able to bring back a warning from an alien civilization previously wiped out by the Goa'uld which simply states "beware the destroyers" followed by a gate address.
- Orbital Bombardment: Apophis' chosen method of attack.
- Self-Destruct Mechanism: The base self-destruct for the SGA, the alternate SGC, reaches zero seconds after Daniel escapes through the gate, killing alternate!Teal'c and everyone else who happened to still be alive on the base.
- Ship Tease: The alternate O'Neill and Carter are engaged.
- Shout-Out: The scene where the Jaffa gain entry to the SGA by blowing through the blast door and battling the defenders is a clear reference to the Stormtroopers boarding Princess Leia’s ship in Star Wars episode four complete with alternate Teal’c playing the role of Darth Vader with his dramatic entry once the firefight was over.
- Taking You with Me: Alt!Carter using a grenade to take down several Jaffa, along with herself.
- There Is No Kill Like Overkill: In revenge for the nuking of Chulak, alternate Teal'c kills alternate O'Neill by shooting him at point-blank range with a Goa'uld staff cannon (the same as mounted on Death Gliders, and previously used within the episode to break through blast doors).
- Trust Password: Daniel pulls this on alternate!O'Neill using the death of his son. Earlier in the episode, he accidentally does the same thing with Catherine, when he makes a passing reference to her long-lost-fiancé Ernest Littlefield in the middle of a rant.
- What Does This Button Do?: The whole mess was ostensibly caused by Daniel thinking it would be a good idea to start fiddling around with random alien artifacts. Although it's a good thing he did, since otherwise there would be no warning about the impending attack on Earth.
